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Temporal variation and ontogenetic shifts in the diet of a surf zone fish, the barred surfperch, Amphistichus argenteus
Full text linkSandy beaches and their associated surf zones support productive food webs that are structured by subsidies from adjacent marine ecosystems. Located at the interface of land and sea, beach ecosystems are characterized by highly dynamic intertidal zonation of mobile macroinvertebrates that varies across time scales ranging from daily and semilunar shifts with tides, to strongly seasonal patterns of beach condition and productivity. Sandy beaches provide an ideal system to examine temporal variation in resource dynamics, an important but understudied dimension of food webs. The barred surfperch, Amphistichus argenteus, is an abundant and widespread surf zone fish in central and southern California that represents an important sport fishery. This live-bearing fish forages on sandy beaches and has been reported to rely primarily upon the intertidal sand crab, Emerita analoga, as prey. However, little is known about the breadth of prey types used by this fish, especially across temporal variation in the supply and accessibility of prey resources on sandy beaches. To address this gap, we investigated variation in the diet of barred surfperch on two temporal scales, season and tide phase, that are known to affect the dynamic distribution of their intertidal prey resources on sandy beaches. Beaches exhibit strong seasonal variation in habitat characteristics that are reflected in populations of intertidal prey for surfperch. We hypothesized that the diet of barred surfperch would respond to seasonal shifts in beach condition and the availability of intertidal macroinvertebrate prey. We also expected that diet could differ with life stage of the fish. To evaluate these questions, we investigated the effect of season on the diet of juvenile and adult barred surfperch, macroinvertebrate prey composition and availability, and relevant environmental variables for two years at Refugio beach. Community composition and the availability of key intertidal prey taxa varied significantly with season. The lower beach crab, Emerita analoga, was important in the diet of barred surfperch and dominated the diet of adult fish in every season, accounting for 92% of their diet. In contrast, juvenile barred surfperch demonstrated strong seasonality in their diet and foraged on prey resources from a wider range of microhabitats, extending from subtidal to upper intertidal zones. The prey resources used by juvenile fish varied with seasonal changes in beach physical characteristics, the population dynamics of key prey species, and species richness of the intertidal macroinvertebrate community. Seasonality in the diet of juvenile fish reveals the dynamic and diverse food web resources supporting populations of barred surfperch.
Semilunar tide phases greatly affect the inundation of intertidal habitats and the distribution of invertebrates on beaches. We hypothesized that the diet of barred surfperch would differ among semilunar tide phases. Specifically, we expected a greater diversity of beach invertebrates would be present in surfperch diet during spring tides that sweep more of the intertidal beach face than during neap tides. To answer this question, we investigated the diet of barred surfperch and the availability of beach prey across semilunar shifts in tidal inundation to explore how fish access prey from a range of intertidal zones at R Beach. Community composition of intertidal invertebrates did not vary with tide phase. Overall, species richness in surfperch diet was positively correlated with species richness of prey on the beach. Increased access to intertidal zones during spring tides increased the diversity of prey used by adult and juvenile barred surfperch, suggesting semi lunar tidal inundation is a mechanism of trophic connectivity across sandy beaches and surf zones. During spring tides, barred surfperch diet included intertidal clams, upper intertidal talitrid amphipods, and a reduced dominance of sand crabs. Diet composition varied significantly with fish life stage through shifts in the use of key prey taxa, supporting our finding of seasonal ontogenetic shifts in diet and underscoring the role of life stage in the food web dynamics of live bearing surf zone fish like surfperch.
Barred surfperch and the intertidal communities that support them reside at a narrow intersection of human impacts and encroaching seas. Sandy beach ecosystems are highly vulnerable to the effects of sea level rise and other manifestations of climate change. These growing threats to beaches and the food webs they support are already being compounded by anthropogenic disturbance and infrastructure at many urban beaches, impacting intertidal biodiversity and beach habitat quality and quantity. Our findings provide new information on the range of prey resources and the dynamics of the intertidal food webs that support populations of this highly valued surf zone fish. Increased understanding of these trophic connections between beaches and surf zones is needed for the challenges facing coastlines in the coming decades
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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Kelp Wrack: Hopping with Life in San Diego County
Full text linkThe same waves that pound the shore off California also tear large amounts of seaweed from the region’s giant kelp forests and rocky reefs. Much of this drift seaweed, known as wrack, is eventually washed ashore. On many of Southern California’s beaches, tractors will remove this wrack (along with trash and litter) and rake the sand, in a process known as beach grooming
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Kelp Wrack: Hopping with Life in Santa Barbara County
Full text linkThe same waves that pound the shore off California also tear large amounts of seaweed from the region’s giant kelp forests and rocky reefs. Much of this drift seaweed, known as wrack, is eventually washed ashore. On many of Southern California’s beaches, tractors will remove this wrack (along with trash and litter) and rake the sand, in a process known as beach grooming
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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Kelp Wrack: Hopping with Life in Los Angeles County
Full text linkThe same waves that pound the shore off California also tear large amounts of seaweed from the region’s giant kelp forests and rocky reefs. Much of this drift seaweed, known as wrack, is eventually washed ashore. On many of Southern California’s beaches, tractors will remove this wrack (along with trash and litter) and rake the sand, in a process known as beach grooming
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Kelp Wrack: Hopping with Life in Ventura County
Full text linkThe same waves that pound the shore off California also tear large amounts of seaweed from the region’s giant kelp forests and rocky reefs. Much of this drift seaweed, known as wrack, is eventually washed ashore. On many of Southern California’s beaches, tractors will remove this wrack (along with trash and litter) and rake the sand, in a process known as beach grooming
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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Kelp Wrack: Hopping with Life in Orange County
Full text linkThe same waves that pound the shore off California also tear large amounts of seaweed from the region’s giant kelp forests and rocky reefs. Much of this drift seaweed, known as wrack, is eventually washed ashore. On many of Southern California’s beaches, tractors will remove this wrack (along with trash and litter) and rake the sand, in a process known as beach grooming
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